This invention relates to sampling apparatus and methods. In one of its aspects this invention relates to inducing flow of gaseous samples from a gaseous environment. In another of its aspects this invention relates to drying moist gaseous samples. In yet another aspect this invention relates to the handling of particulate matter collected from a moist gaseous medium. In yet another aspect of the invention it relates to the prevention of deposition of solid particulate matter on the walls of a sample collection probe.
Sample probes for the collection of gaseous samples or gaseous samples containing particulate matter are well known in the art. It has become common practice to induce a flow into a sample collecting probe from a surrounding gaseous medium by directing motive air flow inside a conduit at a high speed so that air is entrained from the surroundings of this flow and a larger flow of air is caused to occur. Often, in using ejector-type sample induction devices, solids materials from the sampled medium collect on the walls of the induction tube. This collection of solids material on the walls is particularly evident when, as in the sampling of sea spray, the sampled material is moist and the motive air tends to dry the solids material that are deposited on the induction tube walls.
The sampling of sea spray has become important in determining the effectiveness of methods for reducing the amount of salt spray taken into the air inlet of turbine drives of large ships and other large machinery such as operating equipment in offshore and seaside processing facilities. The sampling of sea spray presents a particularly difficult problem because determination of the salt content of the spray depends on obtaining a representative sample of a material, salt, that is generally in solution in the moisture in the spr;ay and from which the moisture content must be reduced sufficiently to provide solid particles for analysis without losing this particulate material by having it stick to the walls of the sample induction tube. The apparatus and method of this invention are most specifically concerned with obtaining representative salt spray samples for analysis of salt content by determining the amount of sodium present.
It has now been found that the sticking of solid particles to the walls of the induction tube can be substantially eliminated by using an air flow amplifier that utilizes the Coanda effect to provide motive gas for sample flow induction. The Coanda effect, named for Henri Coanda who is a developer of devices utilizing the physical principle that bears his name, is that a flowing fluid will attach itself to an adjacent wall and wall then change directions in accordance with the wall's contours. The Coanda effect can be demonstrated both for liquids and gases. By inducing flow into a sample probe by utilizing the Coanda effect in air flow amplification a barrier of motive air travels along the induction tube wall while allowing mixing of the motive gases with the sampled material for reduction of the relative humidity in the sample. The sample is dried while being kept from contacting the walls of the conduit.
It has also been determined that representative samples of salt spray are best obtained using isokinetic sampling techniques so that there is no disturbance of flow of the stream to be sampled at the point of sampling. The velocity of the sample entering the probe must be the same as the velocity of the ambient gaseous environment. Isokinetic sampling is a well-known procedure and has established limits on sample probe inlet design. It is necessary to take a sample through a knife edge on the front end of a probe with the leading edge of the probe sloping away from the knife edge formed by the inner circumference of the probe at an angle of 30.degree. or less.
Since the apparatus and method provided herein will satisfy conditions for obtaining representative samples of solid particulate matter from moist gaseous environments, the method and apparatus are also appropriate for use in obtaining samples of any gaseous environment.
It is therefore an object of this invention to provide apparatus and method for obtaining representative particulate samples from moist, gaseous environments. It is also an object of this invention to obtain representative samples from moist, gaseous environments containing liquid droplets of solutions of crystallizable chemical compounds. It is another object of this invention to provide a sampling probe using motive gas to shield the walls of the probe from contact with the induced sample flow.
Other aspects, objects, and the various advantages of this invention will become apparent upon study of this specification, the drawing, and the appended claims.